Sega SC-3000 Repair
Defect:
- The graphics of the games is not displayed correctly.
- The BASIC cartridge does not work.
Replaced Components:
- 2 x MCM4517-15 RAM (IC12/IC13).
Note:
I have replaced the two RAM MCM4517-15 with a classic RAM 4164 (also used in the Commodore 64) paying attention to short-circuit the pin 9 and 10 of the 4164 RAM.
The MCM4517-15 RAM are 16,384 Words x 1 bit while the 4164 is 65,536 x 1 bit, both are PINOUT compatible except for the pin 9 which in the MCM4517-15 is not used while in 4164 is A7.
This “tricks” to short-circuit the pin 9 and 10 instead of using a resistor of pull-down is also used in some coin-op arcade boards that use the same RAM.
Gallery of the repair:
The TI 99/4A Flash ROM Cartridge, or FlashROM 99 for short, is a cartridge for the TI 99/4A home computer that allows for running ROM cartridge images stored on an SD card.
The FlashROM 99 supports ROM-only images of up to 32K that use the write-to->60xx bank switching scheme. It will not work with programs using GROMs or CRU-based bank switching. The cartridge does not require the Peripheral Expansion Box and runs on both PAL and NTSC consoles.
FlashROM 99 is released as Open Source Hardware under the CERN OHL license and the GNU GPL license. Both hardware design files and firmware sources are available on GitHub.
The project homepage is hosted at GitHub.
Gallery:
Download: FlashROM 99 SD Card (1126)
source: endlos99.github.io/flashrom99 ti99iuc.it
Texas Instruments TI-99/4A – Navarone’s Widget Multi Cartridges Fixed.
Works that have been made:
- Annoying short circuit under the cartridge connector on the slot 3 between the pins: 4,6,8,10
Repair Commodore 64 (ASSY 250407) 1 of 6
Asserted defect:
- Sometimes works, sometimes not, check solder.
Fix:
I state now that this Commodore 64 has been socketed.
The work done is not bad but was better clean up the remaining flux around the pcb pads, the eye wants its part.
The defect occurred twice on 55 switching on and off (i counted them)
In one of these two times i have noticed the problem that was missing the CPU Output Clock on the solder side pad. I redid the solder and fixed the socket pin and everything worked again.
I also noticed that one of the eight RAM it was warmer than the other, but working, i have decided to replace it. I don’t exclude that this operation has only fixed one of the problems, the other might to be the power supply that i don’t have.
I have twisted several times the PCB on itself, i dropped down at least 10 times on the table and leave power on for four hours, now i can exclude solder problems.
In the photos you will see a PLA 906114 (U17) that for some bizarre reason have solder it on the socket, really curious.
Gallery of the repair:
Repair Commodore 64 (ASSY 250425) 2 of 6
Asserted defect:
Defects found:
- Missing the Composite Video Signal.
- Black Screen.
- Missing Audio.
Repair:
- Replaced 1 x MOS 8701 Clock Generator (U31)
- Replaced and Socketed 1 x MOS 906114 PLA (U17)
- Replaced 1 x MOS 6581 SID (U18)
Gallery of the repair:
Repair Commodore 64 (ASSY 250407) 3 of 6
Asserted defect:
Defects found:
Repair:
- Replaced and Socketed 1 x MOS 906114 PLA (U17)
Gallery of the repair:
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PPI Super Sketch for Texas Instruments TI-99 Repair.
Defect:
- The cartridge is not recognized by the TI-99/4A.
Repair:
- Replaced 1 x 74LS139 (U1)
- Replaced 1 x 74LS30 (U2)
Note:
The repair of the Super Sketch cartridge was quite simple, in the first time i thought a problem of the ROM but instead the failure was the two IC U1 and U2, which should do the work of the Bank Switching.
To remove the two IC i have preferred to cut the pins and then remove each pin because i know very well this type of PCB and also lowering the temperature there is a risk that the pitches come off.
Gallery of the repair:
Easy replacement of the Commodore Amiga Mouse push-buttons.
Gallery:
ORIC-1 Repair [1 of 2]
Defect:
- Garbage boot Screen and then another Garbage screen (see photo).
Repair:
- Replaced 1 x CPU 6502 (IC5)
- Replaced 1 x RAM HM4864P (IC12)
Gallery of the repair:
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ORIC-1 Repair [2 of 2]
Defect:
Repair:
- Replaced 1 x Electrolytic Capacitor interrupted of 220uF 10v (C1)
Gallery of the repair:
Commodore 64 (ASSY 250407) Repair
Defect:
- Black screen and a noisy background sound .
Repair:
- Replaced 1 x MOS 906114 (PLA) U17
- Replaced 1 x MOS 6581 (SID) U18
Commodore Amiga 500 (ASSY 312510) Repair
Defect:
- Garbage boot Screen (see photo).
Repair:
- Replaced 1 x FAT Agnus 8371
Gallery of the repair:
Commodore Amiga 600 – External Floppy Drive as DF0.
This mod is very easy, just follow the schematic attached to this post.
Gallery:
Schematic:
Works that have been made:
- Cleaning the leaked acid (KONTAKT PLCC)
- Sprayed a thin layer of insulating lacquer (DUE-CI V-66)
Gallery:
2 x Texas Instruments TI-99/4 Power Supply Fixed
- Removed the RIFA Filter Capacitor, one exploded.
Gallery:
Texas Instruments TI-99/4 Fixed
Defect:
- Garbage screen on startup immediatly or after a couple of minutes.
Fix:
- This defect is very similar to the one of the Coleco Vision console.
The problem are the pins oxidized of the power switch, i have sprayed R-11 and the problem it’s disappeared completely.
I left turned on the computer for more than 2 hours and i have made a 50 x power cycle (ON/OFF) and the problem is no longer appeared.
Note:
I thought there had to be a VDP RAM problem with a diagnosis made remotely without having the TI-99/4 in the laboratory.
To avoid using the lame RF modulator i have used a standard Commodore 64 composite cable that works very well with a NTSC composite video output.
Gallery:
Commodore 64G repaired (1 of 2)
Defect:
Repair:
- Replaced 1 x MOS 7707 (7406) U8
Note:
- The motherboard has been repaired several times, the technician probably in a previous life was a butcher.
Commodore 64 repaired (2 of 2)
Defect:
- Garbage screen but runs programs perfectly.
Repair:
- Replaced 1 x MOS 906114 (PLA) U17
Apple Computer 1, also known later as the Apple I, or Apple-1, was released by the Apple Computer Company (now Apple Inc.) in 1976. It was designed and hand-built by Steve Wozniak. Wozniak’s friend Steve Jobs had the idea of selling the computer.
The Apple I was Apple’s first product, and to finance its creation, Jobs sold his only means of transportation, a VW Microbus, and Wozniak sold his HP-65 calculator for $500. It was demonstrated in July 1976 at the Homebrew Computer Club in Palo Alto, California.
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Apple 1 (Mimeo / Mike Willegal Clone) Assembled for a friend of mine; Paolo Cognetti.
Many thanks for the Technical & Moral support to: Piero Todorovich and Alessandro Polito.
I also thank for some electronic components: Gabriele Molesto Zaverio of Museo Dell’informatica Funzionante, Piero Todorovich.
I had several problems with this Apple 1 clone, i very briefly describe the problems below and i attach some photos of the assembling stages.
- 1 – No video image, all voltages are ok.
- 1 + MPS3704 Transistor failure replaced with a 2N3704 pinout not compatible.
- 2 – Garbage screen during boot.
- 2 + Replaced 2 of 7 Shift Register 2504V
- 3 – Keyboard inputs not working, the WOZ monitor is freezed and shows an “@ \” but the “\” does not wrap.
- 3 + Replaced a 27k resistor half broken, probably during transport the capacitor has crushed the resistor.
- 4 – The keyboard does not respond correctly, typing A they print @, typing 1 they print 0 … and so on …
- 4 + Keyboard adapter from Apple II/+ to Apple 1 in short circuit. A wire is skewered in a pin of a Socket.
- 5 – The computer does not respond correctly, but it seems to work. The WOZ monitor responds to commands but does not write to memory and print random locations.
- 5 + Replaced a 7410 which had a pin always at high level.
- 6 – The keyboard has several problems, some switches are completly dead.
- 6 + Replaced switches.
Photos of the assembling stages:
Video:
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